Multibyte patterns in `scanf` are handled incorrectly

The following program is incorrect, as `scanf` reads 2 bytes from `stdin` and writes them to `p`:
```c
int main() {
  char* p = "Hello";
  scanf("%2c", p);
  if (p[1] != 'e') reach_error();
}
```

However, ULTIMATE currently report this program as correct, as only one single byte is written, since the patern is simply ignored.